1. Field of the Invention
The present invention relates to a technique for updating a program while maintaining security in a key-installed system or an LSI device used for such a system.
2. Description of the Related Art
Conventionally, for the purpose of protecting a program for operating an LSI device from fraudulent processing, a program encrypted with a predetermined manufacturer key is stored in a memory and decrypted with the key for execution. However, with such a system, a program encrypted with a common manufacturer key is executed in a large number of LSI devices, and thus, if information of the manufacturer key is fraudulently leaked even from a single product, it becomes possible to commit tampering of programs in a large number of products. Therefore, the security cannot be improved.
In a method conceived for the purpose of overcoming such a problem, a program for operating LSI devices is encrypted with an inherent key unique to each LSI device, and a product can execute only a program encrypted with an inherent key unique to the product (see Japanese Patent Applications Nos. 2002-215096 and 2002-258481). Such a method improves the security because fraudulent leakage of key information from a single product causes no effect on the other products. As a premise of this method, a method for encrypting a key twice was conceived (see Japanese Unexamined Patent Publication No. 2003-101527).
In general, updating of a program installed in a product LSI device is achieved by securing a safe communication path by an SSL connection and transmitting a raw program or a program encrypted with a manufacturer key from a server to the LSI device. However, with this method, if the communication path is fraudulently accessed, a program executable in a large number of products can be fraudulently read out, so that the security in program update is not improved.
In the case where the above method is used for the purpose of overcoming such a problem, a raw program or a program encrypted with a manufacturer key cannot be executed in an LSI device without any additional processing because the LSI device executes only a program encrypted with its own inherent key.
In another possible method, programs encrypted with different keys for respective LSI devices are prepared in a server and key information is managed for each LSI device. The programs encrypted with different keys for respective LSI devices are transmitted from the server to the LSI devices. However, this method requires enormous efforts and cost and therefore is not practical.